Recently, a gas discharge display unit (plasma display panel) has been utilized as a plane-type display unit for an information terminal such as a portable computer. The gas discharge display unit has been applied widely because the display is clear and the angle of visibility is greater than that of a liquid crystal panel.
Furthermore, the size of a television picture receiver has been increased so that a projection-type television using a projection cathode ray tube or a liquid crystal panel has been marketed. However, the brightness of the screen and the size of the device have caused problems.
On the other hand, the coloring technology of the gas discharge display unit has recently been developed remarkably. The depth of the unit can be reduced more than that of the cathode ray tube. Consequently, attention has been paid to the gas discharge display unit as the best wall-type television for high visibility. In addition, it is expected that colors will be accurately reproduced and that brightness and lifetime will be enhanced.
An example of a memory driving type DC gas discharge display unit according to the prior art will be described below with reference to FIG. 8. As shown in FIG. 8, a plurality of stripe-shaped cathode electrodes 22 are formed on a front plate 21, which is made of a transparent glass or the like. A plurality of stripe-shaped anode buses 24a are formed on a back plate 23, which is made of a transparent glass or the like. The front plate 21 is opposed to the back plate 23 with a plurality of partition walls 25 held therebetween in such a manner that the cathode electrodes 22 are orthogonal to the anode buses 24a. Thus, a lot of discharge cells 26, which are surrounded by the partition walls 25, are formed like a matrix. The peripheral portions of the front plate 21 and the back plate 23, which are combined, are sealed by a low melting point glass or the like. Discharge gases whose main component is an inert gas are filled in the discharge cell 26.
Anode electrodes 24b are individually formed corresponding to respective discharge cells 26 on the back plate 23. A display electrode 27 is formed on each anode electrode 24b in the discharge cell 26. The display electrode 27 is connected to the anode bus 24a by a resistor 28. Thus, a pair of discharge electrodes are formed in the discharge cell 26 by the cathode electrodes 22 and the display electrode (anode) 27. In FIG. 8, the reference numeral 31 designates an auxiliary electrode for generating auxiliary discharge so as to easily start discharge in the discharge cell 26.
A layer insulating film 30 is formed on the back plate 23, except for the display electrode 27 portion, on which the anode bus 24a, the anode electrode 24b and the resistor 28 are formed. Consequently, discharge can be prevented from occurring between a plasma in the discharge cell 26 and the anode bus 24a or resistor 28. A phosphor 29 is applied onto the layer insulating film 30 in the discharge cell 26 except for the display electrode 27 portion.
The front plate 21 is transparent except for the cathode electrode 22 portion. The surface of the phosphor 29 can be directly observed through the discharge cell 26.
The cathode electrode 22, the anode bus 24a, the anode electrode 24b, the display electrode 27, the resistor 28, the layer insulating film 30, the phosphor 29, the partition wall 25 and the like are formed, by thick film printing technology, on the front plate 21 or the back plate 23 which is made of the glass plate or the like.
In order to increase the pixel density and reproduce the finer images in the above structure similarly to the high visibility television, it is necessary to form partition walls forming discharge cells hyperfinely. More specifically, the partition wall having a height of 160 to 200 .mu.m and a width of 50 to 60 .mu.m should be formed. In particular, 1 dot should be formed by three discharge cells R, G and B in order to display color images. Hence, if fine images are to be displayed, it is necessary to form partition walls having a very small size and highly precise dimensions.
A method for forming the partition walls of a gas discharge display unit according to the prior art will be described with reference to the drawings. FIGS. 9(a) to 9(c) are views showing the steps of forming partition walls in the gas discharge display unit according to the prior art. FIG. 10 is a view schematically showing the sand blasting step. In FIGS. 9(a) to 9(b) and 10, the components that are not related to the formation of partition walls are omitted.
As shown in FIG. 9(a), a rib paste 32 for forming a partition wall 25 is applied, by the knife coating method, onto a back plate 23 made of a transparent glass or the like on which an anode electrode 24b is formed. Then, the rib paste 32 is dried and solidified. Then, a photosensitive film 33 is fixed onto the rib paste 32 as shown in FIG. 9(b). Thereafter, ultraviolet rays are irradiated on the photosensitive film 33 through an exposure mask on which partition patterns are formed, and the sensitized portion is developed and removed to form a mask pattern 34 as shown in FIG. 9(c). As shown in FIG. 9(d), abrasive particles such as glass beads are jetted on the rib paste 32 by means of a sand blasting device having a jet gun 35. Consequently, the rib paste 32 is cut except for the portion on which the mask pattern 34 is formed. Finally, the mask pattern 34 is removed by using a peeling agent as shown in FIG. 9(e). Thus, the partition walls (25) are formed on the back plate 23.
As shown in FIG. 10, the back plate 23 is moved in one direction and the sand blasting device (jet gun 35) reciprocates in the direction perpendicular to the direction of movement of the back plate 23 above the mask pattern 34 on the back plate 23. In this state, the abrasive sand such as glass beads are jetted through the nozzle of the jet gun 35. Consequently, the rib paste 32 on the portion where the mask pattern 34 is not formed is cut and removed.
In order to fabricate the gas discharge display unit according to the prior art, a material for the partition wall is applied over the whole glass substrate by the thick film printing technology, and unnecessary portions are removed at the sand blasting step so that the partition wall is formed. In other words, the material for the partition wall should have the following characteristics: (1) adhesion to the glass substrate, (2) cutting properties for the sand blasting step, (3) adhesion to a resist for a mask during sand blasting, (4) durability against a peeling agent used for peeling and removing the resist after the rib paste is cut, and the like. However, it is very hard for the material for the partition wall material according to the prior art to satisfy all these characteristics.
According to the partition wall having the above structure and the method for manufacturing the same, the shape and dimension of the partition wall have limitations, that is, a width of (100.+-.10) .mu.m and a height of (200.+-.5) .mu.m. In addition, the pitch of the discharge cells is at best (650.+-.10) .mu.m. Accordingly, it is very hard to form fine partition walls and discharge cells having high densities for forming pixels that can reproduce images with high precision.
According to the method for manufacturing the gas discharge display unit according to the prior art, the rib paste is generally cut and removed by sand blasting by means of a sand blasting device having a jet gun. FIG. 11 shows the influence on the cutting rate of the rib paste and the amount of side etching of the partition wall by the jet pressure of the abrasive sand which is applied during sand blasting by means of the jet gun. FIG. 12 shows the influence on the cutting rate of the rib paste and the amount of side etching of the partition wall exerted by the distance between the rib paste and the jet gun (jet distance). As shown in FIG. 11, when a jet pressure P is raised, a cutting rate Rs of the rib paste is increased and the amount Es of side etching of the partition wall is increased at a greater ratio than the cutting rate Rs. If the jet pressure P is set to a relative value having a smaller amount Es of side etching, i.e., 3 or less so that the injection distance must be reduced so as to raise the cutting rate Rs, the amount of side etching is increased again as shown in FIG. 12. As shown in FIG. 13(a), the partition wall 25 should have a rectangular shape in section. However, the partition wall 25 has a concave curved face so that the width of the section on the central portion thereof is reduced. For this reason, the precision and strength of the partition wall are reduced.